org.jboss.util
Class LRUCachePolicy

java.lang.Object
  |
  +--org.jboss.util.LRUCachePolicy

All Implemented Interfaces:

CachePolicy, Service

Direct Known Subclasses:

LRUEnterpriseContextCachePolicy

public class LRUCachePolicy

extends java.lang.Object

implements CachePolicy

Implementation of a Least Recently Used cache policy.

Version:

$Revision: 1.8 $

Author:

Simone Bordet (simone.bordet@compaq.com)

Inner Class Summary

class	LRUCachePolicy.LRUCacheEntry Double linked cell used as entry in the cache list.
class	LRUCachePolicy.LRUList Double queued list used to store cache entries.

Field Summary

protected LRUCachePolicy.LRUList	m_list The linked list used to implement the LRU algorithm
protected java.util.HashMap	m_map The map holding the cached objects
protected int	m_maxCapacity The maximum capacity of this cache
protected int	m_minCapacity The minimum capacity of this cache

Constructor Summary

LRUCachePolicy()
Creates a LRU cache policy object with zero cache capacity.

LRUCachePolicy(int min, int max)
Creates a LRU cache policy object with the specified minimum and maximum capacity.

Method Summary

protected void	ageOut(LRUCachePolicy.LRUCacheEntry entry) Callback method called when the cache algorithm ages out of the cache the given entry.
protected void	cacheMiss() Callback method called when a cache miss happens.
protected LRUCachePolicy.LRUCacheEntry	createCacheEntry(java.lang.Object key, java.lang.Object value) Factory method for cache entries
protected LRUCachePolicy.LRUList	createList() Factory method for the linked list used by this cache implementation.
void	destroy() Destroys the cache that is now unusable.
void	flush() Flushes the cached objects from the cache.
java.lang.Object	get(java.lang.Object key) Returns the object paired with the specified key if it's present in the cache, otherwise must return null.
void	init() Initializes the cache, creating all required objects and initializing their values.
void	insert(java.lang.Object key, java.lang.Object o) Inserts the specified object into the cache following the implemented policy.
java.lang.Object	peek(java.lang.Object key) Returns the object paired with the specified key if it's present in the cache, otherwise must return null.
void	remove(java.lang.Object key) Remove the cached object paired with the specified key.
void	start() Starts this cache that is now ready to be used.
void	stop() Stops this cache thus flush()ing all cached objects.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

m_map

protected java.util.HashMap m_map

The map holding the cached objects

m_list

protected LRUCachePolicy.LRUList m_list

The linked list used to implement the LRU algorithm

m_maxCapacity

protected int m_maxCapacity

The maximum capacity of this cache

m_minCapacity

protected int m_minCapacity

The minimum capacity of this cache

Constructor Detail

LRUCachePolicy

public LRUCachePolicy()

Creates a LRU cache policy object with zero cache capacity.

See Also:

init()

LRUCachePolicy

public LRUCachePolicy(int min,
                      int max)

Creates a LRU cache policy object with the specified minimum and maximum capacity.

See Also:

init()

Method Detail

init

public void init()
          throws java.lang.Exception

Initializes the cache, creating all required objects and initializing their values.

Specified by:

init in interface Service

See Also:

start(), destroy()

start

public void start()
           throws java.lang.Exception

Starts this cache that is now ready to be used.

Specified by:

start in interface Service

See Also:

init(), stop()

stop

public void stop()

Stops this cache thus flush()ing all cached objects.
After this method is called, a call to start() will restart the cache.

Specified by:

stop in interface Service

See Also:

start(), destroy()

destroy

public void destroy()

Destroys the cache that is now unusable.
To have it working again it must be re-init()ialized and re-start()ed.

Specified by:

destroy in interface Service

See Also:

init()

get

public java.lang.Object get(java.lang.Object key)

Description copied from interface: CachePolicy

Returns the object paired with the specified key if it's present in the cache, otherwise must return null.
Implementations of this method must have complexity of order O(1). Differently from CachePolicy.peek(java.lang.Object) this method not only return whether the object is present in the cache or not, but also applies the implemented policy that will "refresh" the cached object in the cache, because this cached object was really requested.

Specified by:

get in interface CachePolicy

Following copied from interface: org.jboss.util.CachePolicy

Parameters:

key - the key paired with the object

See Also:

CachePolicy.peek(java.lang.Object)

peek

public java.lang.Object peek(java.lang.Object key)

Description copied from interface: CachePolicy

Returns the object paired with the specified key if it's present in the cache, otherwise must return null.
Implementations of this method must have complexity of order O(1). This method should not apply the implemented caching policy to the object paired with the given key, so that a client can query if an object is cached without "refresh" its cache status. Real requests for the object must be done using CachePolicy.get(java.lang.Object).

Specified by:

peek in interface CachePolicy

Following copied from interface: org.jboss.util.CachePolicy

Parameters:

key - the key paired with the object

See Also:

CachePolicy.get(java.lang.Object)

insert

public void insert(java.lang.Object key,
                   java.lang.Object o)

Description copied from interface: CachePolicy

Inserts the specified object into the cache following the implemented policy.
Implementations of this method must have complexity of order O(1).

Specified by:

insert in interface CachePolicy

Following copied from interface: org.jboss.util.CachePolicy

Parameters:

key - the key paired with the object

object - the object to cache

See Also:

CachePolicy.remove(java.lang.Object)

remove

public void remove(java.lang.Object key)

Description copied from interface: CachePolicy

Remove the cached object paired with the specified key.
Implementations of this method must have complexity of order O(1).

Specified by:

remove in interface CachePolicy

Following copied from interface: org.jboss.util.CachePolicy

Parameters:

key - the key paired with the object

See Also:

CachePolicy.insert(java.lang.Object, java.lang.Object)

flush

public void flush()

Description copied from interface: CachePolicy

Flushes the cached objects from the cache.

Specified by:

flush in interface CachePolicy

createList

protected LRUCachePolicy.LRUList createList()

Factory method for the linked list used by this cache implementation.

ageOut

protected void ageOut(LRUCachePolicy.LRUCacheEntry entry)

Callback method called when the cache algorithm ages out of the cache the given entry.
The implementation here is removing the given entry from the cache.

cacheMiss

protected void cacheMiss()

Callback method called when a cache miss happens.

createCacheEntry

protected LRUCachePolicy.LRUCacheEntry createCacheEntry(java.lang.Object key,
                                                        java.lang.Object value)

Factory method for cache entries